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Licensed Unlicensed Requires Authentication Published by Oldenbourg Wissenschaftsverlag November 21, 2014

Kinetics of the Reactions of Hydroxyl Radicals with Diacetylene and Vinylacetylene

Jörg Sommerer and Matthias Olzmann

Abstract

Highly unsaturated hydrocarbons like diacetylene (C4H2) or vinylacetylene (C4H4) are important intermediates in combustion that can have impact on soot formation. One of their major loss channels is reaction with hydroxyl radicals (OH). We studied the reactions C4H2 + OH → products (1) and C4H4 + OH → products (2) in a quasi-static reactor with helium as bath gas. The hydroxyl radicals were produced by laser flash-photolysis of nitric acid at a wavelength of 248 nm and detected by laser-induced fluorescence with excitation at 282 nm. The rate coefficients were obtained from the intensity-time profiles under pseudo-first order conditions with respect to OH. We found a virtually temperature-independent rate coefficient for reaction (1): k1 = (1.0 ± 0.3) × 10−11 cm3 s1 (T = 290–670 K, P = 2.7–30.5 bar) and a weakly negative temperature-dependent rate coefficient for reaction (2): k2(T) = (6.4 ± 1.9) × 10−12 exp (486 K/T) cm3 s1 (T = 295–740 K, P = 1.7–19.2 bar). For neither of the two reactions pressure dependence was observed. From comparisons with analogous reaction systems, we conclude that the dominating reaction pathway is OH addition, where in the case of C4H4 the double bond is preferred over the triple bond.

Acknowledgement

Financial support by the Deutsche Forschungsgemeinschaft (SFB 606 “Non-stationary Combustion: Transport Phenomena, Chemical Reactions, Technical Systems”) is gratefully acknowledged. We thank Isabelle Weber for help with the experiments.

Received: 2014-9-18
Accepted: 2014-10-22
Published Online: 2014-11-21
Published in Print: 2015-4-28

©2014 Walter de Gruyter Berlin/Boston